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postgresql/src/backend/optimizer/path/joinrels.c

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/*-------------------------------------------------------------------------
*
* joinrels.c
* Routines to determine which relations should be joined
*
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.82 2006/12/12 21:31:02 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "optimizer/joininfo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
static List *make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels);
static List *make_rels_by_clauseless_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels);
static bool has_join_restriction(PlannerInfo *root, RelOptInfo *rel);
/*
* make_rels_by_joins
* Consider ways to produce join relations containing exactly 'level'
* jointree items. (This is one step of the dynamic-programming method
* embodied in make_one_rel_by_joins.) Join rel nodes for each feasible
* combination of lower-level rels are created and returned in a list.
* Implementation paths are created for each such joinrel, too.
*
* level: level of rels we want to make this time.
* joinrels[j], 1 <= j < level, is a list of rels containing j items.
*/
List *
make_rels_by_joins(PlannerInfo *root, int level, List **joinrels)
{
List *result_rels = NIL;
List *new_rels;
ListCell *r;
int k;
/*
* First, consider left-sided and right-sided plans, in which rels of
* exactly level-1 member relations are joined against initial relations.
* We prefer to join using join clauses, but if we find a rel of level-1
* members that has no join clauses, we will generate Cartesian-product
* joins against all initial rels not already contained in it.
*
* In the first pass (level == 2), we try to join each initial rel to each
* initial rel that appears later in joinrels[1]. (The mirror-image joins
* are handled automatically by make_join_rel.) In later passes, we try
* to join rels of size level-1 from joinrels[level-1] to each initial rel
* in joinrels[1].
*/
foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
if (level == 2)
other_rels = lnext(r); /* only consider remaining initial
* rels */
else
other_rels = list_head(joinrels[1]); /* consider all initial
* rels */
if (old_rel->joininfo != NIL)
{
/*
* Note that if all available join clauses for this rel require
* more than one other rel, we will fail to make any joins against
* it here. In most cases that's OK; it'll be considered by
* "bushy plan" join code in a higher-level pass where we have
* those other rels collected into a join rel.
*/
new_rels = make_rels_by_clause_joins(root,
old_rel,
other_rels);
/*
* An exception occurs when there is a clauseless join inside a
* construct that restricts join order, i.e., an outer join or
* an IN (sub-SELECT) construct. Here, the rel may well have join
* clauses against stuff outside its OJ side or IN sub-SELECT, but
* the clauseless join *must* be done before we can make use of
* those join clauses. So do the clauseless join bit.
*
* See also the last-ditch case below.
*/
if (new_rels == NIL && has_join_restriction(root, old_rel))
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
}
else
{
/*
* Oops, we have a relation that is not joined to any other
* relation. Cartesian product time.
*/
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
}
/*
* At levels above 2 we will generate the same joined relation in
* multiple ways --- for example (a join b) join c is the same
* RelOptInfo as (b join c) join a, though the second case will add a
* different set of Paths to it. To avoid making extra work for
* subsequent passes, do not enter the same RelOptInfo into our output
* list multiple times.
*/
result_rels = list_concat_unique_ptr(result_rels, new_rels);
}
/*
* Now, consider "bushy plans" in which relations of k initial rels are
* joined to relations of level-k initial rels, for 2 <= k <= level-2.
*
* We only consider bushy-plan joins for pairs of rels where there is a
* suitable join clause, in order to avoid unreasonable growth of planning
* time.
*/
for (k = 2;; k++)
{
int other_level = level - k;
/*
* Since make_join_rel(x, y) handles both x,y and y,x cases, we only
* need to go as far as the halfway point.
*/
if (k > other_level)
break;
foreach(r, joinrels[k])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
ListCell *r2;
/*
* We can ignore clauseless joins here, *except* when there are
* outer joins --- then we might have to force a bushy outer
* join. See have_relevant_joinclause().
*/
if (old_rel->joininfo == NIL && root->oj_info_list == NIL)
continue;
if (k == other_level)
other_rels = lnext(r); /* only consider remaining rels */
else
other_rels = list_head(joinrels[other_level]);
for_each_cell(r2, other_rels)
{
RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
if (!bms_overlap(old_rel->relids, new_rel->relids))
{
/*
* OK, we can build a rel of the right level from this
* pair of rels. Do so if there is at least one usable
* join clause.
*/
if (have_relevant_joinclause(root, old_rel, new_rel))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, new_rel);
/* Avoid making duplicate entries ... */
if (jrel)
result_rels = list_append_unique_ptr(result_rels,
jrel);
}
}
}
}
}
/*
* Last-ditch effort: if we failed to find any usable joins so far, force
* a set of cartesian-product joins to be generated. This handles the
* special case where all the available rels have join clauses but we
* cannot use any of the joins yet. An example is
*
* SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
*
* The join clause will be usable at level 3, but at level 2 we have no
* choice but to make cartesian joins. We consider only left-sided and
* right-sided cartesian joins in this case (no bushy).
*/
if (result_rels == NIL)
{
/*
* This loop is just like the first one, except we always call
* make_rels_by_clauseless_joins().
*/
foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
if (level == 2)
other_rels = lnext(r); /* only consider remaining initial
* rels */
else
other_rels = list_head(joinrels[1]); /* consider all initial
* rels */
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
result_rels = list_concat_unique_ptr(result_rels, new_rels);
}
/*----------
* When OJs or IN clauses are involved, there may be no legal way
* to make an N-way join for some values of N. For example consider
*
* SELECT ... FROM t1 WHERE
* x IN (SELECT ... FROM t2,t3 WHERE ...) AND
* y IN (SELECT ... FROM t4,t5 WHERE ...)
*
* We will flatten this query to a 5-way join problem, but there are
* no 4-way joins that make_join_rel() will consider legal. We have
* to accept failure at level 4 and go on to discover a workable
* bushy plan at level 5.
*
* However, if there are no such clauses then make_join_rel() should
* never fail, and so the following sanity check is useful.
*----------
*/
if (result_rels == NIL &&
root->oj_info_list == NIL && root->in_info_list == NIL)
elog(ERROR, "failed to build any %d-way joins", level);
}
return result_rels;
}
/*
* make_rels_by_clause_joins
* Build joins between the given relation 'old_rel' and other relations
* that are mentioned within old_rel's joininfo list (i.e., relations
* that participate in join clauses that 'old_rel' also participates in).
* The join rel nodes are returned in a list.
*
* 'old_rel' is the relation entry for the relation to be joined
* 'other_rels': the first cell in a linked list containing the other
* rels to be considered for joining
*
* Currently, this is only used with initial rels in other_rels, but it
* will work for joining to joinrels too.
*/
static List *
make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
List *result = NIL;
ListCell *l;
for_each_cell(l, other_rels)
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
if (!bms_overlap(old_rel->relids, other_rel->relids) &&
have_relevant_joinclause(root, old_rel, other_rel))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, other_rel);
if (jrel)
result = lcons(jrel, result);
}
}
return result;
}
/*
* make_rels_by_clauseless_joins
* Given a relation 'old_rel' and a list of other relations
* 'other_rels', create a join relation between 'old_rel' and each
* member of 'other_rels' that isn't already included in 'old_rel'.
* The join rel nodes are returned in a list.
*
* 'old_rel' is the relation entry for the relation to be joined
* 'other_rels': the first cell of a linked list containing the
* other rels to be considered for joining
*
* Currently, this is only used with initial rels in other_rels, but it would
* work for joining to joinrels too.
*/
static List *
make_rels_by_clauseless_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
List *result = NIL;
ListCell *i;
for_each_cell(i, other_rels)
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(i);
if (!bms_overlap(other_rel->relids, old_rel->relids))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, other_rel);
/*
* As long as given other_rels are distinct, don't need to test to
* see if jrel is already part of output list.
*/
if (jrel)
result = lcons(jrel, result);
}
}
return result;
}
/*
* has_join_restriction
* Detect whether the specified relation has join-order restrictions
* due to being inside an outer join or an IN (sub-SELECT).
*/
static bool
has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
{
ListCell *l;
foreach(l, root->oj_info_list)
{
OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms preserve their ordering */
if (ojinfo->is_full_join)
continue;
/* anything inside the RHS is definitely restricted */
if (bms_is_subset(rel->relids, ojinfo->min_righthand))
return true;
/* if it's a proper subset of the LHS, it's also restricted */
if (bms_is_subset(rel->relids, ojinfo->min_lefthand) &&
!bms_equal(rel->relids, ojinfo->min_lefthand))
return true;
}
foreach(l, root->in_info_list)
{
InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
if (bms_is_subset(rel->relids, ininfo->righthand))
return true;
}
return false;
}
/*
* make_join_rel
* Find or create a join RelOptInfo that represents the join of
* the two given rels, and add to it path information for paths
* created with the two rels as outer and inner rel.
* (The join rel may already contain paths generated from other
* pairs of rels that add up to the same set of base rels.)
*
* NB: will return NULL if attempted join is not valid. This can happen
* when working with outer joins, or with IN clauses that have been turned
* into joins.
*/
RelOptInfo *
make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
{
Relids joinrelids;
JoinType jointype;
bool is_valid_inner;
RelOptInfo *joinrel;
List *restrictlist;
ListCell *l;
/* We should never try to join two overlapping sets of rels. */
Assert(!bms_overlap(rel1->relids, rel2->relids));
/* Construct Relids set that identifies the joinrel. */
joinrelids = bms_union(rel1->relids, rel2->relids);
/*
* If we have any outer joins, the proposed join might be illegal; and in
* any case we have to determine its join type. Scan the OJ list for
* conflicts.
*/
jointype = JOIN_INNER; /* default if no match to an OJ */
is_valid_inner = true;
foreach(l, root->oj_info_list)
{
OuterJoinInfo *ojinfo = (OuterJoinInfo *) lfirst(l);
/*
* This OJ is not relevant unless its RHS overlaps the proposed join.
* (Check this first as a fast path for dismissing most irrelevant OJs
* quickly.)
*/
if (!bms_overlap(ojinfo->min_righthand, joinrelids))
continue;
/*
* Also, not relevant if proposed join is fully contained within RHS
* (ie, we're still building up the RHS).
*/
if (bms_is_subset(joinrelids, ojinfo->min_righthand))
continue;
/*
* Also, not relevant if OJ is already done within either input.
*/
if (bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
bms_is_subset(ojinfo->min_righthand, rel1->relids))
continue;
if (bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
bms_is_subset(ojinfo->min_righthand, rel2->relids))
continue;
/*
* If one input contains min_lefthand and the other contains
* min_righthand, then we can perform the OJ at this join.
*
* Barf if we get matches to more than one OJ (is that possible?)
*/
if (bms_is_subset(ojinfo->min_lefthand, rel1->relids) &&
bms_is_subset(ojinfo->min_righthand, rel2->relids))
{
if (jointype != JOIN_INNER)
{
/* invalid join path */
bms_free(joinrelids);
return NULL;
}
jointype = ojinfo->is_full_join ? JOIN_FULL : JOIN_LEFT;
}
else if (bms_is_subset(ojinfo->min_lefthand, rel2->relids) &&
bms_is_subset(ojinfo->min_righthand, rel1->relids))
{
if (jointype != JOIN_INNER)
{
/* invalid join path */
bms_free(joinrelids);
return NULL;
}
jointype = ojinfo->is_full_join ? JOIN_FULL : JOIN_RIGHT;
}
else
{
/*----------
* Otherwise, the proposed join overlaps the RHS but isn't
* a valid implementation of this OJ. It might still be
* a valid implementation of some other OJ, however. We have
* to allow this to support the associative identity
* (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab
* since joining B directly to C violates the lower OJ's RHS.
* We assume that make_outerjoininfo() set things up correctly
* so that we'll only match to the upper OJ if the transformation
* is valid. Set flag here to check at bottom of loop.
*----------
*/
is_valid_inner = false;
}
}
/* Fail if violated some OJ's RHS and didn't match to another OJ */
if (jointype == JOIN_INNER && !is_valid_inner)
{
/* invalid join path */
bms_free(joinrelids);
return NULL;
}
/*
* Similarly, if we are implementing IN clauses as joins, check for
* illegal join path and detect whether we need a non-default join type.
*/
foreach(l, root->in_info_list)
{
InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
/*
* This IN clause is not relevant unless its RHS overlaps the proposed
* join. (Check this first as a fast path for dismissing most
* irrelevant INs quickly.)
*/
if (!bms_overlap(ininfo->righthand, joinrelids))
continue;
/*
* If we are still building the IN clause's RHS, then this IN clause
* isn't relevant yet.
*/
if (bms_is_subset(joinrelids, ininfo->righthand))
continue;
/*
* Cannot join if proposed join contains rels not in the RHS *and*
* contains only part of the RHS. We must build the complete RHS
* (subselect's join) before it can be joined to rels outside the
* subselect.
*/
if (!bms_is_subset(ininfo->righthand, joinrelids))
{
bms_free(joinrelids);
return NULL;
}
/*
* At this point we are considering a join of the IN's RHS to some
* other rel(s).
*
* If we already joined IN's RHS to any other rels in either input
* path, then this join is not constrained (the necessary work was
* done at the lower level where that join occurred).
*/
if (bms_is_subset(ininfo->righthand, rel1->relids) &&
!bms_equal(ininfo->righthand, rel1->relids))
continue;
if (bms_is_subset(ininfo->righthand, rel2->relids) &&
!bms_equal(ininfo->righthand, rel2->relids))
continue;
/*
* JOIN_IN technique will work if outerrel includes LHS and innerrel
* is exactly RHS; conversely JOIN_REVERSE_IN handles RHS/LHS.
*
* JOIN_UNIQUE_OUTER will work if outerrel is exactly RHS; conversely
* JOIN_UNIQUE_INNER will work if innerrel is exactly RHS.
*
* But none of these will work if we already found an OJ or another IN
* that needs to trigger here.
*/
if (jointype != JOIN_INNER)
{
bms_free(joinrelids);
return NULL;
}
if (bms_is_subset(ininfo->lefthand, rel1->relids) &&
bms_equal(ininfo->righthand, rel2->relids))
jointype = JOIN_IN;
else if (bms_is_subset(ininfo->lefthand, rel2->relids) &&
bms_equal(ininfo->righthand, rel1->relids))
jointype = JOIN_REVERSE_IN;
else if (bms_equal(ininfo->righthand, rel1->relids))
jointype = JOIN_UNIQUE_OUTER;
else if (bms_equal(ininfo->righthand, rel2->relids))
jointype = JOIN_UNIQUE_INNER;
else
{
/* invalid join path */
bms_free(joinrelids);
return NULL;
}
}
/*
* Find or build the join RelOptInfo, and compute the restrictlist that
* goes with this particular joining.
*/
joinrel = build_join_rel(root, joinrelids, rel1, rel2, jointype,
&restrictlist);
/*
* Consider paths using each rel as both outer and inner.
*/
switch (jointype)
{
case JOIN_INNER:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_INNER,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_INNER,
restrictlist);
break;
case JOIN_LEFT:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_LEFT,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_RIGHT,
restrictlist);
break;
case JOIN_FULL:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_FULL,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_FULL,
restrictlist);
break;
case JOIN_RIGHT:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_RIGHT,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_LEFT,
restrictlist);
break;
case JOIN_IN:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_IN,
restrictlist);
/* REVERSE_IN isn't supported by joinpath.c */
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_INNER,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_OUTER,
restrictlist);
break;
case JOIN_REVERSE_IN:
/* REVERSE_IN isn't supported by joinpath.c */
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_IN,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_OUTER,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_INNER,
restrictlist);
break;
case JOIN_UNIQUE_OUTER:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_OUTER,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_INNER,
restrictlist);
break;
case JOIN_UNIQUE_INNER:
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_INNER,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_OUTER,
restrictlist);
break;
default:
elog(ERROR, "unrecognized join type: %d",
(int) jointype);
break;
}
bms_free(joinrelids);
return joinrel;
}
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